The groups would receive standard OPV doses at birth, at 6 weeks, at 10 weeks and at 14 weeks of age, as recommended by the expanded program of immunization (EPI). As practiced by WHO and UNICEF, OPV doses would also be administered in the cohort, through the polio mass vaccination campaign, scheduled twice in every 3 months. The zinc and placebo preparation will be administered in equal volumes (2.5 ml daily), prepared by Atco Laboratories Limited, one of the leading pharmaceutical industries in Pakistan. . They would hold the allocation codes, replenish supplies at fortnightly intervals and maintain consumption records. The research and monitoring staff will be fully blinded to these preparations.